This invention relates to a wire connecting structure of a lamp unit mounted in a lamp mounting window formed in an interior wall member covering a vehicle body panel, and more particularly to an improvement for preventing characteristics of electrical connection between a wire connecting terminal portion and a wire from being degraded by the influence of heat generated by a bulb.
In the case of mounting a lamp unit, such as a room lamp and a courtesy lamp, on an interior wall member, such as a roof trim and a door trim, covering a vehicle body panel of a vehicle, the lamp unit has heretofore been mounted in a lamp mounting window formed in the interior wall member.
FIGS. 5 to 7 show a wire connecting structure of a related lamp unit disclosed in JP-A-6-79044U and others.
The lamp unit 1, shown in FIG. 5, is a room lamp unit for mounting on a ceiling portion of a vehicle room, and this lamp unit comprises an insulating housing 3 for mounting in a lamp mounting window in a roof trim, serving as an interior wall member of the ceiling portion, a generally-cylindrical bulb 5, having a pair of electrodes 5a and 5b provided respectively at its opposite ends, a wire connecting conductor 7, having a wire connecting terminal portion 7a for connection to a wire 6, installed on the roof trim, and a bulb contact 7b, electrically connected to one electrode 5a of the bulb 5, a switch unit 9 for switching an operating condition of the bulb 5, and a switch connecting conductor 11 electrically connecting the other electrode 5b of the bulb 5 to the switch unit 9.
As shown in FIG. 6, the bulb 5 is mounted on that side (upper surface in this Figure) of the insulating housing 3 facing the vehicle room, and a releasable cover lens 15 is mounted on this housing, and then this housing is mounted on the roof trim.
The switch unit 9 has a switch lever 16 pivotally supported on the insulating housing 3, and by pivotally moving this switch lever, a contact 16a, formed at a distal end of this switch lever, can be contacted with a selected one of mating conductors, thereby switching the operating condition of the bulb 5.
The wire connecting conductor 7 and the switch connecting conductor 11 are bus bars formed of an electrically-conductive metal sheet.
As shown in FIG. 7, the wire connecting terminal portion 7a of the wire connecting conductor 7 is in the form of a tongue-like tab terminal which can be fittingly connected to a female terminal of a connector 18 secured to a distal end of the wire 6.
In the above related lamp unit 1, the wire connecting portion, formed by the connector 18, is disposed as close to the one electrode 5a of the bulb 5 as possible so that the length of installation of the wire connecting conductor 7 can be reduced as much as possible, as shown in FIG. 7.
Therefore, in the lamp unit 1 in which the distance between the bulb 5 and the connector 18 is short, heat, generated when the bulb 5 is lighted, is liable to be transferred to the connector 18 through the wire connecting conductor 17, so that this connector 18 is liable to be affected by this heat. The terminal fitting portion of the connector 18 is subjected to stress relaxation due to the heat, and therefore there has been a fear that the pressure of contact between the terminals is lowered, so that the electrical resistance increases.
It is therefore an object of this invention to overcome the above problem, and more specifically to provide a wire connecting structure of a lamp unit in which a wire connection portion, at which a wire connecting terminal portion and a wire are connected together, is less liable to be affected by heat generated at the time of lighting of a bulb, thereby securing a connection reliability.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
(1) A structure for connecting wire to a lamp unit mounted to a lamp mounting window formed in an interior wall member covering a vehicle body panel, the structure comprising:
an insulating housing mounted to the lamp mounting window;
a bulb which includes a first electrode and a second electrode and is attached to the insulating housing;
a wire connecting conductor which includes a wire connecting terminal portion for connection to the wire installed on a vehicle body panel-side of the interior wall member, and a first bulb contact portion electrically connected to the first electrode; and
a switch connecting conductor which includes a switch contact portion connected to a switch unit for switching an operating condition of the bulb, and a second bulb contact portion electrically connected to the second electrode,
wherein relative positional relation between the first electrode and the second electrode is so determined that the first electrode is disposed remote from the wire connecting terminal portion so as to increase a radiating area extending between the wire connecting terminal portion and the first bulb contact portion.
(2) The structure according to (1), wherein the wire connecting conductor is constituted by a first conductor including the wire connecting terminal portion, and a second conductor which is separate from the first conductor and includes the first bulb contact portion.
(3) The structure according to (1), wherein the first bulb contact portion is a power supply-side bulb contact portion, and the second bulb contact portion is a grounding-side bulb contact portion.
(4) The structure according to (1), wherein length from the wire connecting terminal portion to the first bulb contact portion is longer than length from the first bulb to the second bulb.
(5) The structure according to (4), wherein a part of the wire connecting conductor extends along the bulb from the first electrode side toward the second electrode side.
(6) The structure according to (2), wherein the first conductor and the second conductor are made of materials different from each other.
In the above construction, the distance or spacing between the wire connecting terminal portion and the power supply-side bulb contact portion of the wire connecting conductor is increased, and by doing so, the radiating area between the wire connecting terminal portion and the power supply-side bulb contact portion is increased, and therefore the amount of radiation of heat from the conductor surface can be increased.
Therefore, heat, generated at the time of lighting of the bulb, is sufficiently radiated at the region extending from the power supply-side bulb contact portion to the wire connecting terminal portion, so that the heating of the wire connecting terminal portion, which is the connecting portion connected to the wire, is suppressed. Therefore, the reliability of the electrical connection of the wire connecting terminal portion is prevented from being decreased by stress relaxation and so on due to the heat.
The first conductor is made of an electrically-conductive material (for example, a copper alloy such as C2600) having excellent electrical conductivity and a suitable degree of ductility, and by doing so, a conductor of the wire can be positively connected to the wire connecting terminal portion even when this wire connecting terminal portion is formed by press-connecting blades, a piercing terminal or the like.
The second conductor is made of an electrically-conductive material (for example, stainless steel such as SUS301 and SUS304) which is hard, and has resilient properties, and by doing so, a proper load of contact of the power supply-side bulb contact portion with the electrode of the bulb can be secured, and therefore the bulb can be positively held against vibrations and an impact.
Therefore, with respect to the wire connecting conductor, by suitably selecting materials for the first conductor and the second conductor which meet different purposes and functions of the wire connecting terminal portion and the power supply-side bulb contact portion, and then by forming the assembly, the reliability of the wire connecting terminal portion and the reliability of the power supply-side bulb contact portion can be achieved at the same time.